Conventionally, in a power source circuit configured as an inverter or the like, a power semiconductor device such as a power MOSFET, a bipolar transistor, an Insulated Gate Bipolar Transistor (IGBT), or the like is used as a switching device. Usually, such power semiconductor devices are packaged in a power module in which one or more of such devices are housed in a package provided with a heat radiating plate or the like. Patent Literature 1 and Patent Literature 2 each describe a conventional example of a power module.
FIG. 8 is a circuit diagram illustrating an example of a power source circuit having a conventional power module.
The power source circuit is a circuit in which an alternating-current voltage supplied from the primary side positioned to the left of the transformer 4 is converted into a direct-current voltage by two power modules 5-1 and 5-2 on the secondary side positioned on the right, by alternately performing ON/OFF switching processes, so as to charge a battery 1 via a choke coil 3 and a capacitor 2. Within the package of each of the power modules 5-1 and 5-2, a MOSFET 5a serving as a switching-purpose power semiconductor device is installed.
Conventionally, when a power module (e.g., the power module 5-1 or 5-2) is used in a power source circuit, a measure is taken in consideration of deteriorations of the power semiconductor device (e.g., the MOSFET 5a) that may be caused by generation of heat due to operations with high electric power. For example, Patent Literature 1 describes a method for detecting deteriorations of solder joint parts by detecting degradation in thermal resistance on the basis of changes in a current value that are observed when a forward current is caused to flow through the power semiconductor device. Patent Literature 2 describes a method for keeping the temperature at joint parts of a semiconductor device equal to or lower than a tolerance value even when a large current flows therethrough, by using a wide band gap semiconductor as a power semiconductor device. Further, in power source circuits such as that illustrated in FIG. 8, another measure is also taken where, for example, a fuse for the purpose of preventing an overcurrent is inserted in the supply path to the battery 1.